1. Field of the Invention
The present invention relates to an ink-jet printhead, and more particularly, to a bubble-jet type ink-jet printhead and manufacturing method thereof.
2. Description of the Related Art
The ink ejection mechanisms of an ink-jet printer are largely categorized into two types: an electro-thermal transducer type (bubble-jet type) in which a heat source consisting of resistive heating elements is employed to form a bubble in ink causing ink droplets to be ejected, and an electro-mechanical transducer type in which a piezoelectric crystal bends to change the volume of ink causing ink droplets to be expelled.
An ink-jet printhead having this bubble-jet type ink ejector needs to meet the following conditions. First, a simplified manufacturing procedure, low manufacturing cost, and high volume production must be offered. Second, to produce high quality color images, creation of satellite droplets that trail ejected main droplets must be prevented. Third, when ink is ejected from one nozzle or ink is refilled into an ink chamber after ink ejection, cross-talk with adjacent nozzles from which no ink is ejected must be prevented. To this end, a back flow of ink in the opposite direction of a nozzle must be avoided during ink ejection. Another heater shown in FIGS. 1A and 1B is provided for this purpose. Fourth, for a high speed print, a cycle beginning with ink ejection ending with ink refill must be as short as possible.
However, the above conditions tend to conflict with one another, and furthermore the performance of an ink-jet printhead is closely associated with the construction of an ink chamber, ink channel, and heater, types of formation and expansion of bubbles, and the relative size of each element.
In efforts to overcome problems with the above requirements, ink-jet print heads having a variety of structures have been proposed in U.S. Pat. Nos. 4,339,762; 4,882,595; 5,760,804; 4,847,630; and 5,850,241, European Patent No. 317,171, and Fan-Gang Tseng, Chang-Jin Kim, and Chih-Ming Ho, xe2x80x9cA Novel Micoinjector with Virtual Chamber Neckxe2x80x99, IEEE MEMS ""98, pp. 57-62. However, ink-jet printheads proposed in the above patents and literature may satisfy some of the aforementioned requirements but not completely provide an improved ink-jet printing approach. Thus, further improvements for an ink-jet printhead remain to be required.
To solve the above problems, it is an objective of the present invention to provide a bubble-jet type ink jet printhead having a structure for satisfying the aforementioned requirements.
It is another objective of the invention to provide a method of manufacturing an ink jet printhead having a structure for satisfying the aforementioned requirements.
It is further an object of the present invention to produce numerous nozzle ejectors on a substrate, wherein an ink manifold supplies ink to each ink ejector by either having ink chambers that join with the manifold or having an ink channel etched in the substrate to carry ink from the manifold to the ink chamber for ejection.
It is further an object of the present invention to provide both anisotropic etching and isotropic etching to achieve the ink jet structures presented in the present invention.
It is further an object of the present invention to provide bubble guides and droplet guides for each nozzle;
It is further an object of the present invention to provide for a hemispherical and an ellipsoid ink chamber for each nozzle;
It is also an object of the present invention to provide circular or elliptical heaters to match the shape of the ink chamber.
Accordingly, to achieve the above objectives, the present invention provides a bubble-jet type ink jet printhead including a substrate integrated with a manifold for supplying ink and an ink chamber, both of which are recessed from the same surface of the substrate, a nozzle plate in which a nozzle is formed, a heater consisting of resistive heating elements, and electrodes for applying current to the heater. The ink chamber connects with the manifold and is a space filled with ink to be ejected. The shape thereof is substantially hemispherical.
The nozzle plate is stacked on the substrate and covers the manifold and the ink chamber. A nozzle is formed at a position corresponding to he center portion of the ink chamber. The heater having a ring shape surrounds the nozzle on the nozzle plate. Furthermore, the ink chamber is directly connected to the manifold or else the ink channel is disposed therebetween. The cross-section of the ink channel is elliptic.
A bubble guide and a droplet guide extending in the depth direction of the ink chamber from the edges of the nozzle is formed for guiding the direction in which the bubble grows and the direction in which an ink droplet is ejected during ink ejection. Furthermore, the heater has a xe2x80x9cCxe2x80x9d or xe2x80x9cOxe2x80x9d shape so that the bubble may be substantially doughnut-shaped.
The present invention also provides a method of manufacturing bubble-jet type ink jet printhead. According to the manufacturing method, a substrate is etched from the surface of the substrate to form an ink chamber and a manifold, thereby integrating the ink-jet printhead with the substrate. More specifically, an insulating layer is formed on the surface of a substrate and a ring-shaped heater and electrodes for applying current to the heater are formed on the insulating layer. The insulating layer is etched to form a opening for an ink chamber having a diameter less than that of the ring-shaped heater and a opening for a manifold on the inside and outside of the heater, respectively; The exposed substrate by the etched insulating layer is etched to form an ink chamber which is of a diameter greater than that of the ring-shaped heater and is substantially hemispherical in shape and a cylindrical manifold. A protective layer in which a nozzle is formed at a location corresponding to the center portion of the ink chamber is deposited over the entire surface of the substrate to cover the manifold.
An anisotropic etch is first performed on the substrate exposed by the etched insulating layer by a predetermined depth and then an isotropic etch is performed on the substrate thereby forming cylindrically shaped ink chamber and manifold. Between the steps of etching the insulating layer and the substrate, an etch mask exposing the opening for an ink chamber is formed on the insulating layer. The substrate exposed by the etch mask and the insulating layer is anisotropically etched by a predetermined depth to form a hole. A spacer is formed along a sidewall of the hole. In this way, a bubble guide and a droplet guide extending in the depth direction of the ink chamber from the edges of the nozzle are formed. The opening for an ink chamber is elliptic, so the ink chamber is substantially cylindrical and the cross-section thereof is elliptic.